Transient Synchronization Stability Analysis of Hybrid Islanded Systems with GFM and GFL Converters

With the continuous expansion of renewable energy installations and the increasing penetration of power-electronicbased devices, the power system is transitioning into a hybrid system combining grid-following and grid-forming converters. In this setup, renewable energy plants operate in both grid-connected and islanded modes. In islanded operation, the frequency and power angle of gridfollowing and grid-forming converters are mutually coupled, making the transient synchronization problem more complex. To precisely analyze the transient response of islanded systems, this paper derives and establishes a third-order nonlinear dynamic model incorporating the frequency difference, power angle difference, and system frequency of a dual-converter system. Unlike grid-connected system, it is found that increasing the inertia coefficient <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$J$</tex> in islanded system effectively enhances transient synchronization stability. Finally, the correctness of mathematical model and effectiveness of increasing the inertia <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$J$</tex> are verified through simulation.